High temperature energy conversion systems require materials having both high strength and high stability at temperatures which soften or oxidize currently available metals. We previously reported development of a two-phase Cr--Nb alloys which were two-phase systems having mechanical properties superior to Ni-based "superalloys" currently used in very high temperature conditions. We described and disclosed in U.S. Pat. No. 5,282,907 systems having five to eighteen percent Nb, one to ten percent Re and 0.5 to 10% Al and up to about 1 percent of any elements selected from V, Ta, Hf, Zr, and Y. These alloys display excellent strength and creep resistance at temperatures up to 1250.degree. C. under compression tests and acceptable oxidation resistance up to 1,000.degree. C. Unfortunately, the fracture strength is less than 50 ksi in tension at 1,000.degree. C. and surface spalling is observed during cyclic oxidation to 1,000.degree. C. These characteristics impose limitations which may not be acceptable in terms of weight, shock resistance and regular exposure to very high temperatures as would occur, for example, in high performance turbine engines which are routinely stopped and started.